循环流化床预热燃烧试验研究及数值模拟

循环流化床预热燃烧过程中,预热燃料在下行燃烧室的燃烧过程至关重要。为了研究预热燃料在下行燃烧室中的流动和燃烧特性,采用计算流体力学软件Fluent,结合试验手段,对不同二次风喷口配风方式下,预热燃料在下行燃烧室的燃烧过程进行试验及数值模拟,对比了不同配风方式下,流动特性、温度特性、组分浓度分布特性以及氮氧化物排放特性的差异。结果表明,预热燃料在下行燃烧室的燃烧过程中,二次风会卷吸烟气在下行燃烧室上部产生回流,稀释反应物,在中心喷口配风时回流区域更大。不同配风方式下,下行燃烧室中的温度分布不同。环形喷口配风时下行燃烧室中的温度峰值为1 459 K,而中心喷口配风时下行燃烧室的温度峰值为1 555 K,同时环形喷口配风时下行燃烧室的高温区域较小,温度分布更加均匀。环形喷口配风时,预热燃料和二次风的混合更加充分,高温煤气和空气的反应更加强烈,有助于燃料的着火及升温。而中心喷口配风时下行燃烧室顶部的CO和H_2等还原性气体浓度较高,有助于还原NO_x。同时较高的温度促进了气化反应,生成更多的CO和H_2,在燃尽风喷入前的区域形成还原性气氛,有助于进一步还原NO_x。二次风中心喷口配风时,更多的氮氧化物被还原,尾部烟气中的NO_x排放浓度为107×10~(-6),二次风环形喷口配风时,尾部烟气中的NO_x排放浓度为121×10~(-6)。     

旁通式循环流化床脱硫塔脱硫特性的数值模拟

应用标准k-ε模型、DPM模型和物质输运与化学反应模型求解了一台旁通式循环流化床脱硫塔内的动量、能量及组分方程,模拟结果和实验数据符合较好.模拟研究了两种脱硫塔的脱硫效率和流动阻力,进一步研究了空床气速和循环倍率对旁通脱硫塔脱硫效率的影响.结果表明,旁通式脱硫塔的脱硫效率和阻力特性要优于无旁路脱硫塔;旁通式脱硫塔的脱硫效率随空床气速的增加呈现先略有增加后降低的趋势;当循环倍率从20增大到50时,脱硫效率随之有明显的增加,当循环倍率大于50时,脱硫效率随循环倍率的增大略有增加.     

流化床煤的气化脱硫及固态产物燃烧特性研究

为进一步优化煤炭洁净利用技术,减少煤炭利用过程中对环境造成的污染,首先,搭建流化床部分气化特性的试验平台,并分析流化床煤的气化特性,为后续脱硫和燃烧特性研究奠定基础;然后,气化脱硫及其固态产物的燃烧特性进行研究,为今后流化床燃烧炉的选型和降低汽化炉的投资成本提供理论支撑。     

循环流化床燃烧数学模型

介绍了有关文献中循环流化床燃烧的数学模型。按照各模型所使用的流体动力学模型的差异，将它们分成了不同的类别。同时也简要介绍了几种目前应用于循环流化就数学模型的气固两相流数值模拟方法。在评述各模型的优缺点和分析目前所存在问题的基础上，初步提出了进一步发展的方向。     

炉内脱硫脱硝超低排放循环流化床燃烧技术

详细介绍某火电厂中炉内脱硝脱硫超低排放循环流化床项目的改造背景,通过专业的研究与调查,提出超低排放循环流化床燃烧技术的应用流程,其流程内容包含科学选择风机类型、安装除尘装置、改进技术参数、改造炉内本体及开展低氮燃烧等,再利用试运行及时观察循环流化床的运行状态,根据改造后的各项数值,确认火电厂锅炉的改造应用效果。     

烟气循环流化床脱硫数值模拟进展及现状分析

介绍了循环流化床半干法烟气脱硫过程气固两相流动和反应特征及其数值模拟方法。对两相流常用的离散颗粒模型、双流体模型的研究进展进行论述,对于四步骤的脱硫模型进行说明,并介绍了耦合流动模型与脱硫模型过程模拟的优缺点。提出对循环流化床脱硫进一步数值模拟的工作重点应集中在颗粒动力学、曳力模型的修正和反应过程细化模拟方面。     

循环流化床脱硫过程流场与反应的数值研究

在常规研究的基础上,本文选用了k-ε双方程两相模型与含湿颗粒反应化学动力学模型结合对循环流化床脱硫过程内部流场与化学反应过程进行了数值模拟计算,并对计算数据进行了分析,模拟的结果对于工程实践具有较好的应用价值。     

循环流化床锅炉掺烧污泥的炉内燃烧数值模拟

针对不同种类污泥在锅炉内的燃烧分析可知,在循环流化床锅炉掺烧污泥生产以及深度脱硫运行过程中,炉内燃烧数值模拟装置一直是重要的组成部分,炉内燃烧数值模拟装置的正常深度脱硫运行对于循环流化床锅炉掺烧污泥的稳定发展具有重要的意义,因此对炉内燃烧数值模拟装置的深度脱硫运行控制以及深度脱硫技术改造应用是保障炉内燃烧数值模拟装置正常深度脱硫运行的重点。     

流化床燃烧/气化装置内射流区特性的多相流数值模拟

从基本的多相流体力学理论出发，全面地分析了气、固流化床燃烧或气化装置内流动特性，建立了流化床内通用的两相流数学模型，通过数值方法求解了基本控制方程组，编写了适合于微机运行的ＣＡＳＩＣＣ软件，给出了设计和放大过程中所关注的一些重要信息     

发展循环流化床燃烧锅炉

<正> 一、引言煤是一种组成复杂、品质各异的固体矿物类燃料,其理化性质和燃烧特性随产地不同而千变万化。在燃烧高灰和(或)高硫煤以及粒度范围较宽、未经筛分的煤时,常常出现很多困难。中国煤炭资源丰富、品种繁多,煤炭的燃烧利用已有数千年的历史,因此在燃用各类煤种方面,积累了很多经验。但是中国目前燃煤设备的总体性能还很差。例如,耗煤量占全国年产总量约1/3的中小型工业锅炉的平均热效率只有60%左右,而电站的发电平均煤耗也超过400g标煤当量/kWh。此外,由于燃     

Mixing and combustion in a shallow coal-limestone fluidized bed combustor

A model based on the Monte Carlo approach was developed to simulate the mixing and combustion behavior of a shallow coal-limestone fluidized bed combustor. The model involved the coupling of two sub-models: a combustion sub-model based on the two-phase concept of fluidization and a mixing sub-model based on our previously developed dynamic mixing model. The combustion sub-model considered both the volatile and char combustion. It assumed that the combustor consisted of three distinct phases, i.e., jet, bubble and emulsion, with combustion occurring only in the emulsion phase. The mixing sub-model considered the upward or downward movement of a coal particle in the bed as being governed by certain probability laws; these laws were, in turn, affected by the bubbling hydrodynamics. In all, the combustor simulation model took into consideration the effects of coal feed rate, coal size distribution, limestone size, air flow rate and combustor temperature on the combustor behavior. The simulation results included the dynamic response of coal concentration profile, coal size distribution, coal particle elutriation rate as well as the mixing status between the coal and limestone particles.     

High temperature desulphurization by fine limestone during staged fluidized‐bed combustion

This paper reviews the SO₂ emission from a 0.3 m² stainless‐steel fluidized‐bed combustor. Fine coal was premixed with fine limestone and fed pneumatically under the bed. The SO₂ emission was found to depend largely on air staging ratio and bed temperature, which agrees with previous observations. The SO₂ emission observed in sorbent‐free tests (reported earlier by Khan and Cibbs, 1995) was found to be proportional to the sulphur content of the fuel when limestone was added, the sulphur capture at a fixed Ca/S molar ratio was dependent on oxygen stoichiometry and bed temperature. Finely sized limestone enhanced the effectivity of the sorbent at low bed temperature and air staging ratio. During staged combustion, the combustion efficiency depended largely on primary air to coal ratio. Around 90% combustion efficiency was observed at 1 m/s fluidizing velocity which was reduced when fluidizing velocity was increased to 1.5 and 2 m/s. This reduction is due to increased elutriation of finer coal particles from the combustor.     

Modelling of circulating fluidized bed combustion of a char

The combustion of a char in the 41 mm ID riser of a laboratory circulating fluidized bed combustor has been investigated at different air excesses and rates of solids (char and sand) circulating in the loop. Riser performance was characterized by an axial oxygen concentration profile as well as by the overall carbon content and particle size distribution. The proposed model accounts for carbon surface reaction, intraparticle and external diffusion, and attrition. External diffusion effects were relevant in the riser dense region where char was potentially entrapped in large clusters of inert solids. Experimental data and results of the model calculations are in satisfactory agreement.     

Devolatilization and combustion of large coal particles in a fluidized bed

Devolatilization and combustion of large particles of Eastern Canadian coals (Evans and Minto), 5-50 mm dia., were studied in a bench-scale atmospheric fluidized bed reactor at 1023-1173 K with 0.5 mm sand particles as the bed material. The devolatilization time, mass loss history, changes in proximate volatiles content and C/H mass ratio, and temperature history at the centre of the particle during devolatilization were determined. The mass loss during devolatilization is correlated with the proximate volatiles content of the parent coal. The devolatilization time is correlated with the initial particle diameter by a power-law relation with an exponent of 1.54-1.64. The results show insignificant effect of superficial velocity on devolatilization.     

流化床甲烷化反应动力学模拟

利用AspenPlus结合Fortran编写的动力学子程序对流化床甲烷化反应进行建模,结果显示该模型与实验值吻合较好。基于该模型考察了不同工艺条件对cH4收率影响,研究表明：随着反应温度升高,CH4收率逐渐降低,压力越小,cH4收率下降越明显;原料气流量对甲烷化反应影响较小,增加流量,CH4收率呈现降低趋势;当氢碳比在2．7—3．0范围内,CH4收率增幅较大,氢碳比大于3．0时,CH4收率增加缓慢。     

A mathematical model of fluidized bed biomass gasification

A mathematical model of biomass gasification in a fluidized bed has been developed. It considers axial variations of concentrations and temperature in the bubble and emulsion phases. The mass balance involves instantaneous oxidation and equilibrium devolatilization of the biomass, kinetics of solid-gas gasification reactions as well as of gaseous phase reactions and interphase mass transfer and gas convection. The energy balance is solved locally for each vertical volume element, and globally on the reactor by iteration on the temperature at the bottom of the bed. Three parameters have been adjusted based on the experimental results: the heat transfer coefficient at the wall, the weighting of the kinetics of the water-gas shift reaction and the fraction of biomass carbon remaining as char after devolatilization. The model is used to simulate a pilot scale (50 kg/h) biomass gasifier, and its predictions compared to experimental measurements. The temperature and gaseous concentrations are estimated with good accuracy for the experiments using a wood feedstock, except for the concentration of hydrogen which is overestimated.     

油泥砂流化焚烧处理系统与运行分析

提出一种采用异密度循环流化床燃烧技术处理油泥砂的方法。该方法能以较低的运行成本对油泥砂进行资源化洁净利用,降低石油开采成本,实现危险污染物的无害化、减量化、规模化、资源化处理,解决环境污染问题。结合工程实际,详细介绍了流化床焚烧处理的工艺流程、技术特点和1台145t／d流化床焚烧锅炉的设计参数和运行特点。     

煤在富氧流化床燃烧条件下汞的析出及形态分布

目前有关于富氧气氛下流化床燃烧汞的形态转化特性的报道还不是很多,因此本文开展了富氧气氛下煤种对汞形态转化特性的影响的实验研究。采用流化床作为实验设备,选用徐州烟煤和淮北烟煤作为实验燃料,研究了空气气氛下不同温度和不同煤种对汞析出规律的影响,富氧气氛下煤种对汞形态转化规律的影响,并深入分析了相应的汞氧化机理。研究结果表明：在空气气氛下,温度的增加会促进汞的氧化,煤中的含硫量对汞的氧化也有影响;在富氧气氛下,徐州烟煤燃烧产生的气态总汞浓度高于淮北烟煤燃烧产生的气态总汞浓度,徐州烟煤的Hg²⁺（g）的分布率也比淮北烟煤的Hg²⁺（g）的分布率高出16%左右,因为徐州烟煤中高含硫量会影响Hg²⁺（g）的分布率;富氧气氛下徐州烟煤的Hg²⁺的分布率低于空气气氛下的,而淮北烟煤的Hg²⁺（g）分布率则与之相反,这与两种煤中硫含量的不同有关。     

A mathematical model for a biological fluidized bed reactor

A physical model is given in the present report for representing a three-phase biological fluidized bed reaction system which consists of microorganism-coated particles, waste water and air. The system is assumed to be well fluidized. The physical model can be represented by two differential equations describing, respectively, the substrate axial dispersion and diffusion/reaction. Numerical values of the physical parameters are selected from the literature or estimated from semi-empirical equations. The governing system equations are solved by an iterative finite-difference scheme. The theoretical predictions are compared with several experimental measurements and the agreement between them found to be very good, validating the physical model reported here.     

Fluidized bed pyrolysis of distilled spirits lees for adapting to its circulating fluidized bed decoupling combustion

Distilled spirits Lees, rich in cellulose, water and N element, are difficult to burn efficiently and cleanly in grate chain stock boiler. The circulating fluidized bed decoupling combustion (CFBDC) was therefore proposed to burn the distilled spirits lees efficiently and with low-NOx emission. The pyrolysis behavior of the distilled spirits lees was investigated in a fluidized bed reactor for optimizing the pyrolysis conditions of the pyrolyzer in CFBDC. The results showed that the distilled spirits lees began to devolatize at 250 °C and at 350–450 °C the tar yield reached its maximum of about 16.3 wt.% (dry base). The chemical oxygen demand (COD) value of the condensed liquid reached its maximum of about 50,000 mg/L at 450 °C. With raising temperature the pyrolysis gas tended to contain more CO and H₂ and less CO₂. The functional groups H-O, aliphatic C-H, aromatic ring, C=O and C-O were all presented in the char generated at low-temperatures, while only the C-O group was identified for the char from the pyrolysis at 650 °C. The article suggested that the pyrolysis for the CFBDC was better around 500 °C so that certain volatiles could remain in the char to sustain stable combustion.